# Pushing down the low-mass halo concentration frontier with the Lomonosov cosmological simulations

## TL;DR

The paper introduces the Lomonosov simulation suite to measure dark matter halo concentrations at very low masses, extending the concentration-mass relation down to $10^7$ $h^{-1} M_\odot$, and develops methods to extrapolate these results to larger volumes.

## Contribution

It provides high-resolution simulations of low-mass halos and a novel technique to extrapolate concentration measurements to larger cosmological volumes.

## Key findings

- Halo concentration-mass relation extended to $10^7$ $h^{-1} M_\odot$
- Environmental effects on halo concentration are small compared to scatter
- Zoom simulations can reliably measure halo concentrations

## Abstract

We introduce the Lomonosov suite of high-resolution N-body cosmological simulations covering a full box of size 32 $h^{-1}$ Mpc with low-mass resolution particles ($2\times10^7$ $h^{-1}\,M_\odot$) and three zoom-in simulations of overdense, underdense and mean density regions at much higher particle resolution ($4\times10^4$ $h^{-1}\,M_\odot$). The main purpose of this simulation suite is to extend the concentration-mass relation of dark matter halos down to masses below those typically available in large cosmological simulations. The three different density regions available at higher resolution provide a better understanding of the effect of the local environment on halo concentration, known to be potentially important for small simulation boxes and small halo masses. Yet, we find the correction to be small in comparison with the scatter of halo concentrations. We conclude that zoom simulations, despite their limited representativity of the volume of the Universe, can be effectively used for the measurement of halo concentrations at least at the halo masses probed by our simulations. In any case, after a precise characterization of this effect, we develop a robust technique to extrapolate the concentration values found in zoom simulations to larger volumes with greater accuracy. All together, Lomonosov provides a measure of the concentration-mass relation in the halo mass range $10^7-10^{10}$ $h^{-1}\,M_\odot$ with superb halo statistics. This work represents a first important step to measure halo concentrations at intermediate, yet vastly unexplored halo mass scales, down to the smallest ones. All Lomonosov data and files are public for community's use.